Experiment No: 9 Metre bridgeDate Aim: To determine the specific resistance of a given wire by using metre bridge.Apparatus: Metre bridge, the given wire galvanometer, DC source, variable resistance box, Screw gauge, connecting wires etc.,Formula: = RA / l Where R is the resistance of the given wire, A is the area of cross section of the wire l is the length of the wire.If X is in the right gap X = R (100- l1) / l1If X is in the left gap X = R l1 / (100-l1)Circuit diagram:

Observation: X in the right gapS.No. R l1 cm100- l1 cmX = R (100-l1) l1

Mean X = X in the left gapS.No. R l1 cm100- l1 cmX = R l1 (100 - l1)

Mean X =

Least count of the screw gauge = 0.01mmZero error = Zero correction =

hS.No

PSR mmHSRCHSRTR= PSR+(CHSR x LC)mm

Mean =

Procedure:Connect the circuit as shown in the diagram. Switch on the circuit. .Adjust the variable resistance say for 1. Check for the opposite deflection in the galvanometer by keeping the jockey at the extreme ends of the metre bridge wire. If there are opposite deflections the circuit connections are correct. Or else check for tightness of the connections, source connections and the correctness of the wiring. Once the connections are found correct, adjust the variable resistance for different values and in each case find the balancing length and record the values in the l1 column. Calculate the X value in each case by using the formula for right gap X and record the values. Find the average X and record. Repeat the whole experiment by keeping the X in the left gap and the variable resistance in the right gap. Calculate the average of the averages obtained in the two cases. Calculate the diameter of the given wire with the help of a screw gauge. Calculate the resistivity of the wire and record.Result: The resistance of the given wire = The resistivity of the given wire = m Sources of error: 1. Connections may be loose. 2.The cross section of the bridge wire may not be uniform.Precautions: 1 Check for tight connections. 2 Do not scratch the wire by sliding the jockey

Experiment 10 Potentiometer internal resistanceDate:Aim: To determine the internal resistance of a given primary cellApparatus: Potentiometer, given cell, galvanometer, variable resistance, rheostat, DC source, plug keys, high resistance ,connecting wires etc.,

Formula: r = R ( l1 l2 ) / l2

Circuit diagram: Procedure: Connect the circuit as shown in the diagram. Switch on key 1. Check for opposite deflections for the extreme ends of the potentiometer wire. If there is no deflection or one side deflection check for the correctness of the connections and their tightness. Find the balancing length l1 by keeping Key 2 open. Record the value. Press Key 2 closed and adjust the R value say for 1 . Find out the balancing length l2 for different values of R determine l2 in each case and record the values. Calculate the internal resistance by using the formula: r = R ( l1 l2 ) / l2. Record the values. Calculate the average internal resistance.

Observation:Balancing length l1 = cmS.No

R

L2 cm

r = R ( l1 l2) l1 cm

1 2 3

4 5 6 7

Result: The internal resistance of the given cell is found to be =

Sources of error: 1.There may be loose connections2.Parallax error may occur in measurement3.Number of the wire in which the balancing point is taken may go wrong Precautions: 1. Avoid parallax2. Check for tight connections3. Count the number of the wire in which the balancing point is observed carefully

Experiment: 11 Metre bridge Laws of resistancesDate Aim: To verify the law of resistances using metre bridge.Apparatus: Metre bridge, the given resistances, galvanometer, DC source, variable resistance box, connecting wires etc.,Formula: Rs = R1+R2 1/Rp = 1/R1+ 1/R2 If unknown resistance X is in the right gap X = R (100- l1) / l1 Where Rs is is the net resistance in series and Rp is the net resistance in parallel and R1 and R2 are the given resistances, R is the variable resistance and the l1 is the balancing length.Circuit diagram:

Observation: R1 in the right gapS.No. R l1 cm100- l1 cmR1 = R (100-l1) l1

Mean R1 =

R2 in the right gapS.No. R l1 cm100- l1 cmR2 = R (100-l1) l1

Mean R2 =

R1 & R2 in series in the right gapS.No. R l1 cm100- l1 cmRs = R (100-l1) l1

Mean Rs =

R1 & R2 in parallel in the right gapS.No. R l1 cm100- l1 cmRp = R (100-l1) l1

Mean Rp =Procedure:Connect the circuit as shown in the diagram. Switch on the circuit with R1 in the right and the variable resistance in the left gap of the metre bridge.. Adjust the variable resistance R say for 1. Check for the opposite deflection in the galvanometer by keeping the jockey at the extreme ends of the metre bridge wire. If there are opposite deflections the circuit connections are correct. Or else check for tightness of the connections, source connections and the correctness of the wiring. Once the connections are found correct, adjust the variable resistance for different values and in each case find the balancing length and record the values in the l1 column. Calculate the R1 value in each case by using the formula for right gap and record the values. Find the average R1 and record. Repeat the whole experiment by keeping the R2 in the right gap. Repeat the experiment with R1 and R2 in series and in parallel in the right gap and record the values. Calculate the net values of resistances in series and in parallel by using the laws of reistances. Compare the calculated values and the experimental values.

Result: The resistance R1= The resistance R2= Resistances in series by experiment = Resistances in series by formula = Resistances in parallel by experiment = Resistances in parallel by formula = Hence the laws are verified.Sources of error: 1. Connections may be loose. 2.The cross section of the bridge wire may not be uniform.Precautions: 1 Check for tight connections. 2 Do not scratch the wire by sliding the jockey Experiment :12 AC SonometerDate:Aim: To find the frequency of the household alternating current by using a sonometer.

Apparatus: Sonometer, Step down transformer, hanger with variable weights, connecting wires, magnet etc.,

Formula: n = (1/2l) T/m Where n is the frequency of AC, l is the vibrating length at resonance, T is the tension in the wire and m is the mass per unit length of the wire. We can modify the formula as follows n = (g/d2)(M/l 2) Where is density of the wire, M is the load in the hanger and d is the diameter of the wire.

Observation: S.No.Load Mkg Vibrating length l cm M l 2 (kg/cm 2)

LoadingunloadingMean

Mean M = l 2

Diameter of the wire: Least count of the screw gauge = 0.01mmZero error = Zero correction = hS.No

PSR mmHSRCHSRTR= PSR+(CHSR x LC)mm

Mean d =Procedure:Connect the terminals of the step down transformer with the ends of the sonometer brass wire with the help of two connecting wires. Adjust the weight on the hanger of the sonometer say for 0.6 kg. Keep the permanent magnet at the centre of the sonometer. Adjust the positions of the knife edges such that they are very close and at equal distances from the magnet on either sides. Switch on the transformer. Move the knife edges slowly away from the magnet. Observe the wire. At one stage it starts vibrating with maximum amplitude. This happens at resonance. i.e., the frequency of the ac and the natural frequency of the wire are equal. Measure the gap between the knife edges as the vibrating length. Note down in the vibrating length loading column. Repeat the experiment by increasing the load in steps of 200 gram. Repeat the experiment by reducing the weight in steps of 200gm and record the values of vibrating length in the unloading column. Calculate the mean vibrating length for each load. Calculate the value of M in each case and record the values. Calculate the mean of last column. l 2 Measure the diameter of the wire with the help of a screw gauge and record the values.Calculate the value of n and record the value.

Result:The frequency of the AC is found to be = hertz

Sources of error:1. There may be loose connections 1. The wire may get heated up due to the current and its resistance1. Knife edges may not be at equi- distant from the magnet.1. The amplitude may not be the exact maximum.

Precautions: 1.Check for tight connections 2.Avoid heating up of the wire by doing the observation fast. 3.Maintain the knife edges always at equal distance from the magnet 4. Try always for the maximum amplitude

Experiment:13 GalvanometerDate:Aim: To find out the resistance of a given galvanometer and to calculate its figure of merit.Apparatus: Given galvanometer, variable resistance boxes, DC source, plug keys, connecting wires etc.,Formula: G = (RS) / ( R-S )R and S are variable resistances and G is the galvanometer resistance Figure of merit of a galvanometer is K = E / (R+G) Where K is figure of merit, E is the emf of the source used and is the deflection made by the galvanometer needle.Circuit diagram: Observation:S.NoR /2S G = RS / R- SK = E / (R+G) A/Div

Procedure: Connect the circuit as shown in the diagram. By keeping K1 closed and K2 open adjust the value of R such that you get some deflection in the galvanometer with even number of divisions. Note down the value of R and in the tabular column. Switch on K2 and adjust the value of S such that the deflection in the galvanometer becomes /2. Note the value of S. Repeat the experiment for different even number values of . Note down the value of emf E of the electric source used. Calculate the values of G and K in each case. Record the values. Find the average values of G and K.

Result: The galvanometer resistance G = The figure of merit of the galvanometer K = A/division

Sources of error: 1. There may be loose connections. 2. There may be parallax error. 3. The resistance may get heated up.

Precautions: 1.Check for tight connections 2.Avoid parallax during observations 3.Do not allow the current for a long time

Experiment:14 Zener DiodeDate: Aim: To draw the characteristic curve of a Zener diode and hence to determine its reverse break down voltage.Apparatus: Zener diode circuit board with voltmeters and ammeters, connecting wires Circuit diagram & Sample graphs:

Procedure:Connect the circuit as shown in the forward bias circuit diagram. Switch on the circuit. Adjust the supply voltage in steps and record the values of the voltage and the corresponding current values. Remove the connections and wire the circuit as shown in the reverse bias circuit. Switch on the circuit and adjust the supply voltage in steps and record the values of the voltage and the corresponding current values in each case. Plot the graphs between V and I for the forward bias and reverse bias observations. Note down the break down voltage for the Zener diode and record.Observation:Least count of the voltmeter = Least count of the ammeter =

Forward bias Reverse biasS.NOPot.Diff VCurrentmA

S.NOPot.Diff VCurrentmA

Result:The reverse bias break down voltage of the Zener diode is = Sources of error:

1.There may be loose connections2. Parallax error may occur3.Diode may get heated up

Precautions: 1. Check for tight connections,2. Avoid parallax3. Make the observations fast and switch of the source when the circuit is not in use.

Experiment: 15 Transistor CharacteristicsDate:Aim: To draw the characteristics curves of an NPN transistor at common emitter mode and to determine its current gainApparatus: Transistor circuit board at common emitter mode with required ammeters and voltmeters, rheostat, connecting wires etc.,Formula: Current gain = Ic / IB Where Ic is the change in collector current and IB is the change in base current Circuit diagram:

Observation:Least count of the ammeter for IB = ALeast count of the voltmeter for VBE = VLeast count of the ammeter for IC = mALeast count of the voltmeter for VCE = V

Input Characters:Output voltage VCE = 4V Output voltage VCE = 6 VS.No.VBE VIB A

S.No.VBE VIB A

Output Characters:Input current IB = 40 A Input current IB = 60 AS.No.VCE VIC mA

S.No.VCE VIC mA

Transfer characteristics: Output voltage = 6 VS.No.IB A IC mAS.NoIB AIC mAS.No.IB AIC mA

1 2 3 4

5 6 7 8

9 10 11 12

Procedure:Connect the circuit as shown in the diagram. Switch on the circuit. To begin with rotate both the potential divider knobs anti clock wise to ensure the zero values are shown by the meters. Input Characters: Adjust the output circuit potential divider knob for an output voltage say 4V. By keeping this output voltage constant, adjust the input potential divider knob gently to increase the input voltage in steps. Note down the various values of input voltages and the corresponding input currents in the tabular column. Repeat the experiment for another steady output voltage say 6V. Bring the knobs to zero value once again. Output Characters: Now by gently adjusting input supply knob, set an input current at 40A. Keeping this fixed at the same value of input current, adjust the output voltage supply knob in steps to get different values of output voltages. Note down the output voltages and the corresponding output currents in the tabular column. Repeat the experiment for another input current say 60 A. Bring the knobs to zero value once again. Transfer Characters: Adjust the output circuit knob for a steady output voltage say 6V.By keeping this steady adjust the input circuit knob in steps to get different input currents. In each case record the input and the corresponding output current values. Draw separate graphs for the input characteristics, output characteristics and transfer characteristic graphs using the data collected. Calculate the current gain from the slope of the transfer characteristic graph.Result: The characteristic curves of the given NPN transistor is drawn. The current gain is found to be = Sources of error:

1.There may be loose connections2. Parallax error may occur3.Transistor may get heated up

Precautions: 1. Check for tight connections,2. Avoid parallax3. Make the observations fast and switch of the source when the circuit is not in use. Activity : 1 Identification of electronic componentsDate :

Aim: To identify the various electronic components from a collectionApparatus: The given components: Diode, Transistor, IC, LED, Capacitor, Resistor etc.,Procedure: From the mixed components identify 1. The one with maximum number of legs. i.e., more than 3 leads, it is an integrated circuit (IC)1. The one with two leads and with color rings on its body is a resistorResistors of different sizes and body colors but all will have color rings1. The one with two leads but with green/ black body color is a diodeThe green diode will have a flat end and another end curved. The black diode will have a silver ring on one end of the body.1. The one with three legs is a transistor. Some transistors have metallic body and some with plastic1. The one with two leads but wrapped with a plastic cover printed with the details of voltage and capacitance value is a capacitor. In a dielectric capacitor the leads will have difference in length. Longer leg is positive terminal and the other is negative1. The one with two leads but transparent body with either white or colored body is an LED. This will also have legs with length difference. Longer is positive and the short one is negative

Result: The given components are identified

Activity : 2 PolaroidsDate:Aim: To study the effect of rotation of one polaroid in front of the otherApparatus: The given PolaroidsProcedure: Hold the set of polaroids in your hand. Stretch your arm towards a glowing white light source or towards the window or door of your lab such that the centres of the polaroids are in line with your eye sight. By keeping one polaroid fixed rotate the other slowly and steadily. Observe the brightness of the light visible to you when you see through the polaroids. You can notice that at one stage there is no light passing through the polaroids. From this position rotate slowly further through a full circle, either clock wise or anticlockwise and observe with care . You can notice that slowly the darkness decreases and maximum brightness is visible at 90 rotation. Then slowly the brightness decreases and maximum darkness is reached at 180. Again the darkness decreases and maximum brightness is reached again at 270. Then for further rotation in the same direction brightness decreases to reach the maximum darkness at 360

Result: The effect of the change in brightness of light passing through polaroids due to the change in angle between the optical axes of two polaroids is observed.

Activity : 3 Potential gradientAim: To determine the potential gradient along the length of a wire Apparatus: Potentiometer, DC source, Rheostat, Plug Key, Voltmeter, Connecting wires etc.,Formula: Potential gradient = V / l Where V is potential difference and l is the length of the wire.Circuit diagram:

Observation:

S.No

PotentialDifferencevolt

Length of the wire (cm)

K = V/ l v/cm

Procedure:Connect the potentiometer circuit as shown in the diagram. Switch on the circuit. Keep the jockey at 50,150,250,350,450,550,650,750,850,950 cm lengths of the potentiometer and record the corresponding potential differences in the voltmeter. Calculate the potential gradient by using the formula k=v/l. Find the average potential gradient. Result: The potential gradient of the potentiometer wire is = v/cm

Activity 4 Glass slabDate:Aim: To study the lateral shift in the path of a light ray in a glass slabApparatus: Drawing board,glass slab, protractor, scale, pencil, drawing sheet etc.,Observation:S.No.Thickness cm Lateral shift cm

Procedure:Fix the drawing sheet on the drawing board. Place the glass slab on the sheet. Mark the outline of the slab with a sharp pencil. Select a point of incidence on the left half of the top line of the slab. Draw a normal at that point. By using a protractor mark 30 angle and draw the incident ray. Fix two pins with sufficient gap between them and with sufficient gap with the slab. Replace the slab on its outline perfectly. See from the other side of the slab. Fix two pins on the other side of the slab by looking through the slab such that the images of the first two pins seen through the slab and the 3rd and 4th pin are aligned as if there is only one pin. Join the positions of the 3rd and 4th pin. Extend the incide4nt ray. Find the lateral shift of the incident ray. Repeat experiment for various faces of the slab. Compare and conclude the relation between the thickness of the glass and the lateral shift.Result: As thickness increases the lateral shift also increases

Activity: 5 Inductance and resistanceDate:Aim: To study the inductance and resistance of a coil of wire by passing ac through a coil.Apparatus: The given coil, iron core, ac source, dc source, connecting wires, voltmeters and ammeters Circuit diagram: Observation:CoreDC VDC I R AC V AC I Reactance

Air

Iron

Procedure: Connect the coil with dc source as shown in diagram 1.Switch on the circuit, measure the volt and current with and without iron core. Calculate the values of resistance in both cases. Repeat the experiment by connecting the coil with an ac source and ac meters. Find the inductive reactance and compare it with the resistance of the coil.Result:Resistance of the coil in DC circuit: with iron core = Without iron core =Reactance of the coil in ac source with iron core = Without iron core =